Diamond and Gemstone Shapes

Did you know that although diamonds are available in all sorts of shapes, when it comes to coloured gemstones, the shape choices are more limited?
 

Have you ever noticed that some stones like sapphires, especially in larger sizes, seem to always be oval or elongated cushion shapes? And so much of tourmaline and aqua is popular in emerald cut styles? But when you look at amethyst and garnet, it is available in any shape and size at very affordable prices.

This is not just a coincidence.

Let’s take a closer look at how gemstones, their rarity and the choice of shapes are connected.

To begin, here is general guide of available gemstone shapes. The facet placement on diamonds and coloured gemstones is different, but the outline stays more or less the same.

A cutter’s experience and skill can transform a dull rough stone into a sparkling gem, perfect for a new jewellery piece. The shape of the gemstones depends greatly on the shape and size of the rough crystal that is available. Some crystals such as tourmaline, aquamarine and sapphires grow long and thin and others are cubic in shape, such as garnets and diamonds. Take a look at this rough crystal chart.

When the rough crystal is elongated, it makes sense to cut shapes such as oval and elongated cushion to save as much weight as possible. The process of cutting rubies and sapphires in round shapes looses the most weight, which is why large round stones are very rare. You will have a much wider choice of options available if you go for an oval or an elongated cushion.

The availability of the rough also plays an important role. For example ruby and padparadscha sapphire rough is very rare, so the cutter will try to maximise the size of the stone he/she can get out of it, even if it results in a slightly uneven oval or a cushion shape with a deep pavilion. Try not to be too critical of the gemstones, they will not be as perfectly cut as diamonds, but the colour will mesmerise you.

On the other hand, quartz and peridot are abundant and grow in large crystals. This is why gemstones such as amethyst, citrine and peridot are readily available in a variety of sizes and shapes, from tiny 1mm round stones, to 2 carat heart or marquise shapes and 5 carat+ oval and cushion shapes, just to name a few.

Another gemstone that I absolutely adore is morganite. It is more expensive than quartz, but also forms in large crystals, with some specimens from Brazil reportedly weighing up to 10kg. Consequently, morganite is available in large variety of shapes and sizes making it perfect for large statement pieces such as cocktail rings as well as smaller jewellery items. But don’t go too small, the smaller the stone, the lighter the colour looks. Larger stones show more saturated colour. I find that stones smaller than 5mm in diameter show little colour. This cocktail set turned out beautifully!

Emeralds are fractured by nature, often showing cracks and fissures. The mining and cutting process itself, can be damaging to the stone and greatly limit the shape of the finished gemstone. Some shapes, such as princess cuts, are just better suited for diamonds, as those sharp corners on coloured gemstones can be much more prone to chipping. That is why you will hardly ever see princess or marquise cut emeralds or sapphires set in jewellery.

By "cutting off" those large sharp corners and creating emerald cut or square emerald cut (sometimes referred to as asscher cut) the gemstone is less like to chip.

Although emeralds are typically cut into emerald cuts, there are some gorgeous examples of oval emeralds, I loved working on this wonderful project below.

Are you worried about inclusions in your gemstones?

Check out my previous blog post Let’s get some clarity on gemstone inclusions

Colour distribution within the crystal affects the final colour. For example, sapphire and amethyst rough often shows uneven colour banding. Although it is generally not viewed as a positive, in the last few years, unusual colours have become popular with clients seeking something a bit different. Take a look at this bi-colour or parti sapphire, isn’t it unique?

Did you know that amethyst and citrine are both members of the quartz family?

Amethyst is a purple variety of quartz and citrine is an orange/yellow variety.

If the quartz crystal displays both colours, the cutter might decide to cut a stone that shows both of these colours, resulting in a gemstone called ametrine.

A similar idea can be seen in tourmaline, where a bi-colour or watermelon tourmaline can be produced from one tourmaline crystal.

Typically, both of these, ametrine and watermelon tourmaline are cut into emerald cuts, to display this colour combination.

The proportions and angles play an important part in the intensity and shade of colour.

If the stone is too deep, the stone will look dark. If it is too flat or shallow, the light will leak out, making the stone look lighter or creating a “window” which is a see-through part in the middle of the stone. Oh yes, the Goldilocks syndrome.

In this example below, should the cutter create a stone that looks visually smaller from the top, having a heavier pavilion (lower part of the stone) but perhaps a darker overall colour? Or should a visually larger, shallower stone be cut? Depending on the quality and type of the stone, it is for the cutters to decide as professionals.

Transparent gemstones are usually faceted and translucent or opaque gemstones such as opal are cut as cabochons to display the play-of-colour and for durability reasons. A cabochon has a rounded, domed top with a flat curved base. Sapphires and chrysoberyl can also be cut into cabochons if they have the potential to show a star or a cat's eye effect, like this star sapphire and cat's eye chrysoberyl below.

As a final note, if you are on a hunt for the perfect coloured gemstone, try not to focus on the shape too much as you might miss out on a beautifully coloured stone by limiting your options to one particular shape.

For any questions or requests, do get in touch with me via Tsarina Gems Homepage

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